1. Field of the Invention
The present invention relates generally to an ink-jet printing apparatus. More specifically, the invention relates to an ink-jet printing apparatus in which a cloth is used as a printing medium and ejecting and a liquid, such as an ink, is ejected on the cloth by employing an ink-jet head so as to perform cloth printing.
2. Description of the Related Art
Conventionally, an ink-jet printing apparatus has been employed as an information output means for an information processing system, such as a copy machine, a facsimile, an electronic typewriter, a wordprocessor, a workstation and so forth, or as an handy or portable output means for a personal computer, a host computer, an optical disk drive, a video apparatus and so forth.
Such ink-jet printing apparatus performs printing of characters and graphic images by ejecting fine droplet of ink through nozzles (hereinafter occasionally referred to as ejection openings). The ink-jet printing apparatus holds advantages of capavility of high resolution and high speed printing. Also, this type of printing apparatus is abruptly spreading for quietness owing to non-impact type printing, ease of color printing by employing multi color inks, and for ease of down-sizing and increasing of a density of pixels constituting a printed image.
Here, it should be appreciated that a word "print" includes providing of ink (printing, image forming, recording, dying and so forth). In view of this, the ink-jet printing apparatus is applicable not only for an information processing field, but also wide industrial fields, such as an apparel industry, in which cloth, yarn, paper, sheet material and so forth are employed as a printing medium receiving the ink.
A cloth printing apparatus employing an ink-jet system, as one example of application, is a technology becoming to be known in the recent years. The cloth printing in this system has advantages of great freedom in an image to be printed and of lower overall cost, because the cloth printing in the ink-jet system requires no original plate of the image to be printed as that required in screen cloth printing to provide. One example of a construction of such ink-jet type cloth printing apparatus has been disclosed in Japanese Patent Application Laid-open No. 212851/1993.
Incidentally, in the ink-jet cloth printing apparatus, it is sometimes required to change the ink depending upon kind of the cloth to be used and/or upon color to be printed. In such case, it becomes necessary to discharge the ink residing in an ink supply system, cleaning of the ink supply system and re-filling the ink supply system with a new ink to be used for next printing.
As discussed in commonly assigned Japanese Patent Application No. 38616/1994, the re-filling operation for the ink supply system is performed by employing a pressurizing mechanism provided in the ink supply system and the ink discharged from the ink supply system is performed by employing an external device. Also, in the above-identified commonly assigned Japanese Patent Application No. 38616/1994, there is described a construction in which, when the ink is changed for an other ink, overall ink supply routes are replaced so as not to require operations for discharging of the residual ink and cleaning of ink supply system.
As one example of the ink supply system in a conventional typical image forming apparatus employing the ink-jet head, an apparatus disclosed in Japanese Patent Application Laid-open No. 89565/1981 has been known. The shown ink supply system includes a first container for preliminarily storing ink to be supplied to a printing head and a second container which temporarily stores ink and which is provided in an ink route for supplying the ink in the first container to the printing head. Depending upon a remaining ink amount detected in the second container, a pump is driven to supply the ink from the first container to the second container to maintain the ink in the second container at a predetermined amount. As a counter measure for excessive supply of the ink caused when the ink from the first container is supplied to the second container, a construction coping with overflow is provided in the second container.
FIG. 1 is a diagrammatic illustration showing another example of the conventional ink supply system in the printing apparatus employing an ink-jet system.
An ink-jet head 1100 ejects, fine ink droplet downwardly in a drawing, through a plurality of ejection openings 1100a. Ink to be ejected by the head 1100 is supplied from a sub-tank 201 via a supply tubes 201a and 201b. To an ink supply passage constituted of the supply tubes 201a and 201b, an air buffer 202 is connected in series. As a result, influence of vibration to be generated in a ink supply system by movement associated with scanning of the ink-jet head 1100 is avoided to prevent ink ejection from becoming unstable to cause fluctuation of printing density and so forth.
In the sub-tank 201, a fan 207a is provided. The fan 207a is driven by a motor 207 to rotate to pressurize the ink within the sub-tank 201 for feeding through the supply tubes 201a and 201b under a pressurized condition. By this, in the tubes 201a, 201b, the ink-jet head 1100 and an ink tube 201c, recirculation of the ink is generated in the direction of a listed order. Thus, ejection failure of the ink due to generation of the bubble or plugging in the ink-jet head 1100 can be recovered or avoided. More specifically, a bubble within the head may be returned to the sub-tank 201 through the ink tube 201c. Also, the ink being in the vicinity of the ejection opening and having increased viscosity is discharged out of the ejection opening due to slight elevation of the pressure due to recirculation as set forth above.
In the air buffer 202, an air discharge opening 202 is provided for maintaining an air amount therein constant. More specifically, in the case that the air amount in the air buffer becomes greater than or equal to a predetermined amount, an air valve 203 is regularly opened when the ink is pressurized by driving of the pressurizing motor 207 to discharge the air through a discharge tube 204 so that the air amount is kept at a constant amount. At this time, when the air amount is appropriate, the ink is discharged through the discharge tube 204. Therefore, the ink level can be constantly maintained.
An ink cartridge 205 which is mounted on the sub-tank 201 is adapted to make the ink flow out when the ink level of the sub-tank 201 descents fellow a lower end of an ink supply tube of the ink cartridge 205. By this, the ink level in the sub-tank 201 can be constantly maintained so that, a negative pressure acting in the ink-jet head can be maintained constant to allow constant ink supply.
It should be noted that the ink-jet head 1100 is detachably loaded with respect to the ink supply system shown in FIG. 1. Therefore, upon exchanging of the head, the head is disconnected at the portion of a connector 206, and exchanged with another head.
However, in either of the ink supply systems of the foregoing two prior art, various problems are encountered as discussed below. In case of the prior art illustrated in FIG. 1, the air buffer is arranged at the intermediate position in the ink supply system in view of stability of ejection of ink. With such constriction, in order to perform liquid level control within the air buffer, a part of ink is inherently discharged together with the air from the apparatus, upon discharging the air. Therefore, an amount of ink to be consumed other than actual printing becomes relatively large to be a cause of rising of the running cost.
Also, as a problem in the conventional construction as set forth above, problems associating with exchanging of the ink-jet head may be arisen. More specifically, upon exchanging of the head, it is required to remove a head filling material as storage liquid sealed in the head for the purpose of certainly provide storing ability in the product distribution, by means of an external jig. In the operation, the filling liquid is exchanged with the ink to be used in the head. Therefore, it is typical to provide a plurality of external jigs, number of which should correspond to the number of colors of the inks so as to avoid color mixing in the ink. This results in high cost. Also, since the jig is used only for exchanging the ink, the ink within the jig may cause fatigue during relatively long interval of exchanging of the ink. In such fatigue ink is used for printing, it may be a cause for lowering of the image quality.
In addition to the problems relating to the construction of the ink supply system as set forth above, problems are arisen by employing the ink supply system with the two containers as in the foregoing prior art in the cloth printing apparatus. More specifically, in the cloth printing apparatus, for the reason of relatively large printing area, a plurality of ink-jet heads each having relatively large number of ink ejection openings are provided, and continuous printing is performed on an elongated cloth. Therefor, the ink consuming amount becomes much greater than a general printer used in an office or so forth. In this case, since it is typical to limit the size of the container within a given range with respect to the cloth printing apparatus, it is frequently caused to supply the ink from the first container to the second container. In such case, in the conventional ink supply system, it is possible to cause overflow of the ink from the second container similarly to the foregoing problem. If the overflown ink is disposed as waste ink, it becomes quite wasteful. On the other hand, when the overflown ink is stored in another container, an extra space becomes necessary. Furthermore, it becomes necessary to provide a construction to return the collected ink to the first container.
Also, as a further problem, upon changing the ink in the above-mentioned cloth printing apparatus, a troublesome operation becomes necessary to discharge the residual ink in the ink supply system and subsequently re-fill new ink after cleaning the ink supply system. Also, in case that a plurality of sets of ink supply systems are combined in place of exchanging of the ink, the cost for the apparatus is risen corresponding to number of the sets to be provided.